A frequently employed prior art AC power line transient suppressor is a low pass filter including a series inductor and shunt capacitor. When a spike on a power line is applied to such a low pass filter there is usually a ringing effect which produces oscillations for a significant percentage of a cycle of the power line voltage. The oscillations occur at a frequency determined by the resonant frequency of the inductor and capacitor forming the low pass filter. The high frequency ringing effects can be dampened by appropriate selection of a Q for the coil. Such dampening, however, introduces substantial dissipation of power line energy supplied to a load connected across the shunt capacitor.
In commonly assigned Montague U.S. Pat. Nos. 4,095,163 and 4,156,838, there is disclosed a circuit which reduces the amplitude and number of cycles of the ringing effect introduced by a low pass filter transient power line suppressor. In the circuit disclosed by the Montague patents, bi-directional breakdown elements are connected in series circuit with a capacitor, with the series circuit being connected in shunt with a load. It has been found that the series circuit including the capacitor and bi-directional breakdown element in shunt with the load causes a considerable decrease in the amplitude and high frequency content of oscillations which occur in response to a transient spike relative to the low pass filter configuration.